1. Field of the Invention
The present invention relates generally to a mobile communication system, and more particularly to an apparatus and method for performing cell selection to a Home cell or a Private network such that only a specific User Equipment (UE) can access the Home cell or the Private network in a mobile communication system including public cells.
2. Description of the Related Art
Universal Mobile Telecommunications Systems (UMTS) is a 3rd Generation (3G) asynchronous mobile communication system operating in Wideband Code Division Multiple Access (WCDMA), based on European mobile communication systems, Global System for Mobile Communications (GSM) and General Packet Radio Services (GPRS).
The 3rd Generation Partnership Project (3GPP) that standardized UMTS is now discussing Long Term Evolution (LTE) as the next generation of UMTS, Evolved UMTS.
The 3GPP LTE is a technology for enabling packet communications at or above 100 Mbps, aiming at commercialization by the year 2010.
For deploying the LTE system, many communication schemes have been proposed. Among them are schemes for reducing the number of nodes on a communication line by simplifying a network configuration or for optimizing radio protocols for radio channels.
FIG. 1 illustrates an Evolved UMTS mobile communication system to which the present invention is applied.
Referring to FIG. 1, an Evolved UMTS Radio Access Network (E-UTRAN) 110 is simplified to a 2-node structure including Evolved Node Bs (ENBs) 120, 122, 124 and an anchor node 130, or ENBs 126 and 128 and an anchor node 132.
A UE 101 is connected to an Internet Protocol (IP) network via the E-UTRAN 110. The ENBs 120 to 128 correspond to legacy Node Bs in the UMTS system and are connected to the UE 101 via radio channels. Compared to the legacy Node Bs, the ENBs 120 to 128 handle more complex duties in the system.
For example, since all user traffic including real-time service such as Voice Over IP (VoIP) is serviced on shared channels in the 3GPP LTE, an entity for collecting the status information of UEs and scheduling them is required and the ENBs 120 to 128 are responsible for the scheduling. Generally, an ENB controls a plurality of cells and performs Adaptive Modulation and Coding (AMC) by selecting a modulation scheme and a channel coding rate for a UE adaptively according to the channel status of the UE.
As with High Speed Downlink Packet Access (HSDPA) and High Speed Uplink Packet Access (HSUPA) in UMTS, or Enhanced Dedicated CHannel (EDCH), the LTE system will use Hybrid Automatic Repeat reQuest (HARQ) between the ENBs 120 to 128 and the UE 101.
Considering that a variety of Quality of Service (QoS) requirements cannot be fulfilled with HARQ, a high layer may perform an outer ARQ between the UE 101 and the ENBs 120 to 128. HARQ is a technique for increasing reception success rate by soft-combining previous received data with retransmitted data without discarding the previous data. High-speed packet communication systems such as HSDPA or EDCH use HARQ to increase transmission efficiency.
To realize a data rate of up to 100 Mbps, it is expected that the LTE system will adopt Orthogonal Frequency Division Multiplexing (OFDM) in a 20-MHz bandwidth as a radio access technology.
To differentiate services from the legacy UMTS system, the 3GPP LTE standard working group is considering using the Home cell or Private network for the LTE system. The Home cell or Private refers to a cell or a network that provides services only to a specific UE or UE Groups.
However, a cell (re)selection method for applying the Home cell or the Private network is yet to be specified and mentioned. Therefore, conventional methods of the legacy UMTS system for cell selection associated with movement of a UE are not viable in a mobile communication system where the Home cell or the Private network co-exist with macro cells (hereinafter public cells), because the conventional cell selection methods do not involve the concept of the Home cell or the Private network, as previously stated.
Another problem with the conventional cell selection in the communication system having the Home cell or the Private network together with the public cells is that all UEs consider the Home cell or the Private network to be identical in a public cell and performs cell selection by a conventional measurement. Accordingly, there exists a need for a more detailed cell selection method, considering the existence of the Home cell or the Private network in the LTE system.